Fe-38Ni-13Co-4.7Nb-1.5Ti-0.4Si超耐熱合金の窒素ガス流雰囲気中の高温窒化挙動

概要

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High-temperature nitridation behavior of an Fe-38Ni-13Co-4.7Nb-1.5Ti-0.4Si superalloy (alloy 909) has been investigated in a flowing nitrogen gas atmosphere at 1073 to 1273K using metallographic, X-ray diffraction and electron probe microanalysis techniques. The scales consist of an external scale and a subscale. The former is composed of reaction products on the alloy. The latter is composed a mixture of in tragranular reaction products and an un-reacted alloy matrix. The reaction products in these scales are identified as TiN, NbN and Nb2N in cluding small amounts of Fe_3O_4, α-Fe_2O_3 and CoFe_2O_4. The rate constants for the subscale formation in this alloy are about 200〜600 times as large as those in CMSX-2, CMSX-6 and SRR99 reported previously. At all the temperatures the external scale and the subscale grow according to a parabolic rate law and apparent activation energies for these scale growth are estimated to be 123 kJ/mol and 158 kJ/mol, respectively. The rate determining diffusion element for subscale growth is considered to be N in the alloy matrix.